COLUMBIA, S.C. - South Carolina Gov. Mark Sanford said he's been having an affair with a woman from Argentina and will resign as head of the Republican Governors' Association.

The married father of four emotionally apologized to his wife, staff and others at a news conference after returning Wednesday from a trip to Argentina that followed a dayslong absence. He staff had said the Republican was hiking on the Appalachian Trail.

Sanford says he met the woman about eight years ago and it became romantic about a year ago. He says his wife and family have known about it for the past five months.

He had been a rumored contender for the 2012 GOP ticket. He's most recently snared headlines for his unsuccessful fight to turn aside federal stimulus cash for his state's schools.